A summary: State and local laws are changing all the time, but in general, full auto weapons have never been illegal in the United States, but they have been in some states/cities. The National Firearms Act, which dates to 1934, requires registration (not licensing); transfer of a full auto weapon requires payment of a $200 tax and approval of the BATFE. In 1986, a change to the law froze further registration of automatic weapons for other than government agencies; the result has been much demand chasing too few legal weapons, and the price has gone way up.